1. Field of the Invention
The present invention relates to a communications apparatus, and more specifically to a communications apparatus applicable to a telecommunications network, such as a sensor network, formed by plural communications node devices spatially distributed to perform wireless data communication therebetween.
2. Description of the Background Art
In recent years, a type of wireless network is demanded in which plural communications channels, or multi-channels, are available to wireless terminals to carry out multiple, simultaneous communications over the different channels.
IEEE (Institute of Electrical and Electronics Engineers) 802.11 DCF (Distributed Coordination Function), an existing standardized system widely applied as a conventional channel access solution in wireless networks, uses a single wireless channel to be shared between neighbor terminals, which may access the channel at random to conduct data communication. In that system, the wireless terminals are thus allowed to use one channel at a time to transmit frames.
A communication method which permits wireless terminals to use several channels is presented by Yosuke Tanigawa, et al., “Multi-Channel MAC Protocols Pursuing Aggressive Use of Vacant Resources”, The Institute of Electronics, Information and Communication Engineers (IEICE), 2009, IEICE Transactions B, vol. J92-B, No. 1, pp. 196 to 206.
In the method described in Yosuke Tanigawa, et al., one control channel and multiple data channels are provided, and in the standby mode the control channel is normally used for waiting reception. A source node, when attempting data transmission, uses the control channel to send out a control packet which includes information about which channel it intends to use for the data transmission. A destination node, when having received the control packet, acknowledges a receipt of the control packet in order and then switches its channel in use to the designated data channel. Upon receipt of the acknowledgement, the source node can transmit data over the data channel. When the transmission is terminated, both of the source and destination nodes switch back to the control channel to wait for reception over the control channel.
The above procedure allows the nodes to use several channels for communication, thereby reducing radio interference to thereby improve throughput over the system. Moreover, Yosuke Tanigawa, et al., is advantageous in that temporal synchronization may not be established between the nodes.
The solution by Yosuke Tanigawa, et al., however, requires a source node to run a reservation sequence, prior to data transmission, for informing a destination node of a data channel to be used for communication. Such a reservation sequence must be performed for each packet transmission. That raises a problem that increasing overhead is not a little in comparison to a case where only data is directly transmitted without running the reservation sequence.